The effects of oxidized and non-oxidized boron on the Mg-B-H nanohydrides transformation in the nearly nanosized powders

Andrzej Calka 

University of Wollongong, Wollongong NSW, Australia
Faculty of Enginneering, University of Wollongong, Wollongong NSW 2522, Australia

Abstract

In this work oxidized and non-oxidized amorphous boron (a-B) powder was mixed with the elemental Mg in the atomic ratio 2:1 with the intent to mechanically synthesize the Mg(BH4)2 complex hydride. The blends were subjected to the controlled reactive mechanical alloying (CRMA) under hydrogen in a magneto-mill up to 200h. In effect, the particle size was refined to the 100-200nm range. Nanocrystalline MgH2 (~6nm crystallite size) has been formed within the particles when an oxidized a-B is used. In contrast, a mixture of MgB2 and an amorphous hydride MgHx (a-MgHx) has been formed when a non-oxidized a-B is used. The XRD pattern for the nearly-nanopowders containing non-oxidized a-B demonstrates the complete disappearance of the MgH2 phase. Instead, the peaks rising above the background can be attributed to MgB2. We are inclined to attribute it to the hydrogen evolution since desorption conducted in a Sieverts-type apparatus revealed ~1.4wt.% of hydrogen release. The XRD pattern for the powder after DSC test exhibited strong peaks from the MgB2 phase. Oxide doping effect on the observed phase transformations is discussed.

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium C, by Andrzej Calka
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-07-25 05:21
Revised:   2009-06-07 00:44
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